Chin-Chuan Cheng

Characteristics of Pd/InGaP Schottky diodes hydrogen sensors

Pd/InGaP hydrogen sensors based on the metal-oxide-semiconductor (MOS) and metal-semiconductor Schottky diodes have been fabricated and systematically studied. The effects of hydrogen adsorption on device performances such as the current-voltage characteristics, barrier height variation, hydrogen coverage, and heat of adsorption are investigated. The studied devices exhibit very wide hydrogen concentration detection regimes and remarkable hydrogen-sensing properties. Particularly, an extremely low hydrogen concentration of 15 ppm H/sub 2//air at room temperature can be detected. In addition, under the presence of oxide layers in the studied MOS device structure, the enhancements of barrier height and high-temperature operating capability are observed. The initial heat of adsorption for Pd/oxide and Pd/semiconductor interface are calculated as 355 and 65.9 meV/atom, respectively. Furthermore, the considerably short response times are found in studied devices.

Investigation of temperature-dependent characteristics of an n/sup +/-InGaAs/n-GaAs composite doped channel HFET

The temperature-dependent characteristics of an n+-InGaAs/n-GaAs composite doped channel (CDC) heterostructure field-effect transistor (HFET) have been studied. Due to the reduction of leakage current and good carrier confinement in the n+-InGaAs/n-GaAs CDC structure, the degradation of device performances with increasing the temperature is insignificant. Experimentally, for a 1 x 100 μm2 device, the gate-drain breakdown voltage of 24.5 (22.0) V, turn-on voltage of 2.05 (1.70) V, off-state drain-source breakdown voltage of 24.4 (18.7) V, transconductance of 161 (138) mS/mm, output conductance of 0.60 (0.60) mS/mm, and voltage gain of 268 (230) are obtained at 300 (450) K, respectively. The shift of Vth from 300 to 450 K is only 13 mV. In addition, the studied device also shows good microwave performances with flat and wide operation regime.

A new Pt/oxide/In/sub 0.49/Ga/sub 0.51/P MOS Schottky diode hydrogen sensor

A new and interesting Pt/oxide/In/sub 0.49/Ga/sub 0.51/P metal-oxide-semiconductor (MOS) Schottky diode hydrogen sensor has been fabricated and studied. The steady-state and transient responses with different hydrogen concentrations and at different temperatures are measured. The presence of dipoles at the oxide layer leads to an extra electrical field and the variation of Schottky barrier height. Even at room temperature, a very high hydrogen detection sensitivity of 561% is obtained when a 9090 ppm H/sub 2//air gas is introduced. In addition, an absorption response time less than 1 s under the applied voltage of 0.7 V and 9090 ppm H/sub 2//air hydrogen ambient is found. The roles of hydrogen adsorption and desorption for the transient response at different temperatures are also investigated.

Characteristics of a new Pt/oxide/In0.49Ga0.51P hydrogen-sensing Schottky diode

A new Pt/oxide/InGaP metal-oxide semiconductor (MOS) Schottky diode has been fabricated and studied. Upon exposure to hydrogen, the steady-state and transient responses under different hydrogen concentrations and temperatures are measured. Due to the inherent property of InGaP material, e.g. the wide energy gap, a wide hydrogen-sensing range as large as 300 K (from room temperature to 600 K) is obtained. Even at room temperature, a very high sensitivity over 500% for 9090 ppm hydrogen in air is acquired. Furthermore, the measured absorption response time is less than 1 s at the applied voltage of 0.7 V and 9090 ppm hydrogen concentration atmosphere condition. Simultaneously, based on the analysis of the variation of barrier height and hydrogen coverage, the characteristics of the studied Pt/oxide/InGaP MOS Schottky diode is in good agreement with the Lundstrom isotherm.

A novel Pd/oxide/GaAs metal-insulator-semiconductor field-effect transistor (MISFET) hydrogen sensor

A novel and high-performance Pd/oxide/GaAs hydrogen sensor based on a metal-insulator-semiconductor field-effect transistor (MISFET) is fabricated and studied. In the presence of the interfacial oxide, high sensitivity and significant increase in output drain current are observed. In the presence of hydrogen, a 2×200 µm2 gate dimension device shows good dc characteristics including high turn-on voltage, an obvious variation of drain current and a short response time. In addition, under the applied voltage of -4 V and 537 ppm hydrogen in air, a very high sensitivity of 9473 is obtained. This performance shows that the device studied has a good potential for high-speed and high-sensitivity hydrogen sensor and MISFET integrated circuit applications.

Temperature-dependent study of a lattice-matched InP/InGaAlAs heterojunction bipolar transistor

In this work, we report the temperature-dependent characteristics of a new InP/InGaAlAs heterojunction bipolar transistor (HBT). In order to improve the dc performance of conventional InGaAs-based single HBTs, the quaternary In/sub 0.53/Ga/sub 0.34/Al/sub 0.13/As with a wider bandgap is employed as the material for both the base and collector layers. Experimentally, the studied device exhibits a relatively high common-emitter breakdown voltage and low output conductance even at high temperature. Based on the breakdown mechanism of avalanche multiplication, the negative temperature dependence of breakdown voltage is attributed to the positive temperature-dependent impact ionization coefficient. Furthermore, the temperature dependence of current gain is investigated and reported. It is believed that the suppression of hole injection current with decreasing temperature is responsible for the opposite variation of current gains at high current levels.

Hydrogen sensing properties of a Pt‐oxide‐Al0.24Ga0.76As high-electron-mobility transistor

The interesting hydrogen sensing performances of a Pt-oxide-AlGaAs (MOS) high electron mobility transistor (HEMT) are studied and demonstrated. The effects of hydrogen adsorption on device performances such as the threshold voltage shift ΔVth, drain saturation current variation ΔIDS, and transient response are presented. ΔVth and ΔIDS decreased with increasing operating temperature. This suggests that, at higher temperature, less hydrogen atoms diffuse through the Pt bulk and reach the interface between the Pt metal and oxide layer resulting from the relatively faster formation rate of hydroxyl on the Pt surface. The response curves of the studied Pt-AlGaAs MOS HEMT show various profiles at different temperatures. The influences of hydrogen concentration and temperature on the interface sites occupied by adsorbed atoms are also studied.

Pd-oxide- Al/sub 0.24/Ga/sub 0.76/As (MOS) high electron mobility transistor (HEMT)-based hydrogen sensor

An interesting hydrogen sensor based on an Al/sub 0.24/Ga/sub 0.76/As Schottky barrier high-electron mobility transistor with a catalytic Pd metal/oxide/semiconductor is fabricated and demonstrated. In comparison with traditional Schottky diodes or capacitance-voltage type hydrogen sensors, the studied device exhibits larger current variation, lower hydrogen detection limit, and shorter transient hydrogen response time. Besides, good hydrogen-sensing properties, such as significant drain current change, threshold voltage shift, and transconductance change of transistor behaviors, are obtained. Therefore, the studied device provides the promise for high-performance solid-state hydrogen sensors, optoelectronic integrated circuits, and microelectromechanical system applications.

Temperature-dependence investigation of a high-performance inverted delta-doped V-shaped GaInP/In/sub x/Ga/sub 1-x/As/GaAs pseudomorphic high electron mobility transistor

A newly designed inverted delta-doped V-shaped GaInP/In/sub x/Ga/sub 1-x/As/GaAs pseudomorphic high electron mobility transistor (PHEMT) has been successfully fabricated and studied. For a 1/spl times/100 /spl mu/m/sup 2/ device, a high gate-to-drain breakdown voltage over 30 V at 300 K is found. In addition, a maximum transconductance of 201 mS/mm with a broad operation regime for 3 V of gate bias (565 mA/mm of drain current density), a very high output drain saturation current density of 826 mA/mm, and a high DC gain ratio of 575 are obtained. Furthermore, good temperature-dependent performances at the operating temperature ranging from 300 to 450 K are found. The unity current gain cutoff frequency f/sub T/ and maximum oscillation frequency f/sub max/ up to 16 and 34 GHz are obtained, respectively. Meanwhile, the studied device shows the significantly wide and flat gate bias operation regime (3 V) for microwave performances.

Characterization of polysilicon resistors in sub-0.25 μm CMOS ULSI applications

The characteristics of polysilicon resistors in sub-0.25 /spl mu/m CMOS ULSI applications have been studied. Based on the presented sub-0.25 /spl mu/m CMOS borderless contact, both n/sup +/ and p/sup +/ polysilicon resistors with Ti- and Co-salicide self-aligned process are used at the ends of each resistor. A simple and useful model is proposed to analyze and calculate the essential parameters of polysilicon resistors including electrical delta W(/spl Delta/W), interface resistance R/sub interface/, and pure sheet resistance R/sub pure/. This approach can substantially help engineers in designing and fabricating the precise polysilicon resistors in sub-0.25 /spl mu/m CMOS technology.